U.S. patent application number 13/155292 was filed with the patent office on 2012-01-19 for method in a wireless repeater employing an antenna array including vertical and horizontal feeds for interference reduction.
This patent application is currently assigned to QUALCOMM Incorporated. Invention is credited to Kenneth M. Gainey, Steven J. Howard, Hakan Inanoglu, James Arthur Proctor, JR..
Application Number | 20120015603 13/155292 |
Document ID | / |
Family ID | 44511731 |
Filed Date | 2012-01-19 |
United States Patent
Application |
20120015603 |
Kind Code |
A1 |
Proctor, JR.; James Arthur ;
et al. |
January 19, 2012 |
METHOD IN A WIRELESS REPEATER EMPLOYING AN ANTENNA ARRAY INCLUDING
VERTICAL AND HORIZONTAL FEEDS FOR INTERFERENCE REDUCTION
Abstract
An echo cancellation wireless repeater with first and second
antenna arrays having vertical and horizontal feed antenna elements
selects a combination of antenna elements for reception and
transmission to reduce interference and improve the quality of
signal reception. In one embodiment, the antenna elements are
switchably connected to transceiver circuits and a combination of
antenna elements is selected based on the best desired performance
result. In another embodiment, the antenna elements are each
connected to its own transceiver circuit and the echo cancellation
repeater performs beamforming in baseband to select a combination
of antenna elements.
Inventors: |
Proctor, JR.; James Arthur;
(Melbourne Beach, FL) ; Gainey; Kenneth M.; (San
Diego, CA) ; Howard; Steven J.; (Ashland, MA)
; Inanoglu; Hakan; (Acton, MA) |
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
44511731 |
Appl. No.: |
13/155292 |
Filed: |
June 7, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12836493 |
Jul 14, 2010 |
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13155292 |
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Current U.S.
Class: |
455/9 ;
455/11.1 |
Current CPC
Class: |
H04B 7/0874 20130101;
H04W 84/047 20130101; H04W 24/10 20130101; H04B 7/15571 20130101;
H01Q 21/28 20130101; H04B 7/0691 20130101 |
Class at
Publication: |
455/9 ;
455/11.1 |
International
Class: |
H04B 7/015 20060101
H04B007/015; H04W 88/04 20090101 H04W088/04; H04W 24/02 20090101
H04W024/02 |
Claims
1. A method to reduce interference in an echo cancellation repeater
for a wireless communication network, the repeater employing a
first antenna array and a second antenna array, each antenna array
including a first set of antenna elements for vertical feed mode
and a second set of antenna elements for horizontal feed mode, the
method comprising: (a) selecting a combination of antenna elements
from the first and second antenna arrays; (b) receiving incoming
receive signals on receiver circuits associated with the selected
antenna elements; (c) generating correlation energy measurements
indicative of correlation of the receive signals and one or more
reference signals; (d) selecting a desired receive signal being a
receive signal with the largest correlated energy level, excluding
receive signals that are feedback signals of the repeater; (e)
calculating antenna weights for the selected antenna elements using
one of an error minimizing algorithm and an adaptive metric
optimization algorithm; (f) determining a performance result
associated with the selected combination of antenna elements; (g)
storing calculated antenna weights and the performance result
associated with the selected combination of antenna elements; (h)
repeating steps (a) to (g) for one or more combinations of antenna
elements from the first and second antenna arrays; and (i)
selecting a combination of antenna elements from the first and
second antenna arrays based on the stored performance results.
2. The method of claim 1, wherein generating correlation energy
measurements indicative of the correlation of the receive signals
and one or more reference signals comprises: generating correlation
energy measurements indicative of correlation of the receive
signals and one or more pilot code phases of a CDMA-based
communication system.
3. The method of claim 1, wherein generating correlation energy
measurements indicative of the correlation of the receive signals
and one or more reference signals comprises: generating correlation
energy measurements indicative of correlation of the receive
signals and one or more scrambling codes of a WCDMA-based
communication system.
4. The method of claim 1, wherein generating correlation energy
measurements indicative of the correlation of the receive signals
and one or more reference signals comprises: generating correlation
energy measurements indicative of correlation of the receive
signals and one or more pilot tones of an OFDM symbol or an OFDM
preamble.
5. The method of claim 1, wherein the receive signals include the
feedback signals of the repeater and selecting a desired receive
signal being a receive signal with the largest correlated energy
level comprises: selecting a desired receive signal being a receive
signal with the largest correlated energy level a given delay prior
to the receive signal with the overall largest correlated power
level, the receive signal with the overall largest correlated power
being a feedback signal and the given delay being a delay through
the repeater.
6. The method of claim 1, wherein calculating antenna weights for
the selected antenna elements using one of an error minimizing
algorithm and an adaptive metric optimization algorithm comprises:
calculating antenna weights in closed form using an error
minimizing algorithm to minimize an error between the desired
receive signal and the reference signal.
7. The method of claim 6, wherein calculating antenna weights in
closed form using an error minimizing algorithm comprises:
calculating antenna weights in closed form using a minimum mean
square error (MMSE) algorithm to minimize a mean square error
between the desired receive signal and the reference signal.
8. The method of claim 1, wherein calculating antenna weights for
the selected antenna elements using one of an error minimizing
algorithm and an adaptive metric optimization algorithm comprises:
calculating antenna weights adaptively for the antenna elements to
maximize a signal-to-noise ratio (SNR) of the desired receive
signal.
9. The method of claim 8, wherein calculating antenna weights
adaptively for the antenna elements to maximize a signal-to-noise
ratio (SNR) of the desired receive signal comprises: calculating
antenna weights recursively using a metric and an adaptive metric
optimization algorithm to optimize the metric, the metric being
indicative of the SNR of the desired receive signal.
10. The method of claim 9, wherein calculating antenna weights
recursively using a metric and an adaptive metric optimization
algorithm comprises: calculating a metric being a ratio of the
correlated power measurement of the desired receive signal to the
sum of the correlated power measurements of some or all of the
other receive signals.
11. The method of claim 10, wherein calculating a metric being a
ratio of the correlated power measurement of the desired receive
signal to the sum of the correlated power measurements of some or
all of the other receive signals comprises: calculating a metric
being a ratio of the correlated power measurement of the desired
receive signal to the sum of the correlated power measurements of
dominant non-desired receive signals, the dominant non-desired
receive signals being the receive signals other than the desired
receive signal having a correlated power level above a
predetermined threshold.
12. The method of claim 9, wherein calculating antenna weights
recursively using a metric and an adaptive metric optimization
algorithm comprises: applying a steepest descent adaptive algorithm
to modify the antenna weights of the antenna elements to optimize
the metric.
13. The method of claim 1, wherein after receiving incoming receive
signals on receiver circuits associated with the selected antenna
elements and before generating correlation energy measurements, the
method further comprises cancelling estimated feedback signals from
the receive signals.
14. The method of claim 13, further comprising: applying the
calculated antenna weights to the receive signals; combining the
weighted receive signals; and amplifying and transmitting the
combined signals as output signals on one of the first and second
antenna arrays.
15. The method of claim 1, further comprising: applying the
calculated antenna weights to the receive signals; combining the
weighted receive signals; cancelling estimated feedback signals
from the combined signals; and amplifying and transmitting the echo
cancelled signals as output signals on the antenna array of the
repeater.
16. The method of claim 1, wherein selecting a combination of
antenna elements from the first and second antenna arrays
comprises: selecting at least one antenna element of the vertical
feed mode and one antenna element of the horizontal feed mode.
17. The method of claim 1, wherein determining a performance result
associated with the selected combination of antenna elements
comprises: determining the performance result based on one or more
performance factors, the one or more performance factors including
one of an amount of feedback signal, a quality of a channel and a
signal-to-noise ratio (SNR) of the receive signal.
18. The method of claim 17, wherein selecting a combination of
antenna elements from the first and second antenna arrays based on
the stored performance results to optimize a desired performance
result comprises: selecting a combination of antenna elements from
the first and second antenna arrays to optimize the desired
performance result based on a combination of antenna elements
having the lowest feedback signal, or a combination of antenna
elements providing a channel with a high degree of ease of feedback
cancellation, or a combination of antenna elements providing a
highest signal-to-noise ratio (SNR) of the receive signal.
19. The method of claim 17, wherein determining the performance
result based on one or more performance factors comprises
determining the performance result based on a weighted sum of one
or more performance factors.
20. A repeater for a wireless communication network, the repeater
employing echo cancellation and employing a first antenna array and
a second antenna array, each antenna array including a first set of
antenna elements for vertical feed mode and a second set of antenna
elements for horizontal feed mode, the repeater comprising: one or
more switches, each switch being coupled to two or more antenna
elements in each of the first and second antenna arrays, the one or
more switches being configured to select one of the two or more
antenna elements coupled thereto; receiver circuits coupled to the
one or more switches to receive incoming receive signals associated
with the selected antenna elements; an antenna element selection
module and an antenna weight computation module configured to
select one or more combinations of antenna elements, to perform
calculations of antenna weights for each selected combination of
antenna elements, to determine a performance result associated with
each selected combination of antenna elements, and to select a
combination of antenna elements from the first and second antenna
arrays based on the performance results; and an antenna weight
application module configured to apply the calculated antenna
weight to condition the receive signals.
21. The repeater of claim 20, wherein the antenna weight
computation module is further configured to generate for each of
the selected antenna elements correlation energy measurements
indicative of correlation of the receive signals and one or more
reference signals, and to select a desired receive signal being a
receive signal with the largest correlated energy level, excluding
receive signals that are feedback signals of the repeater, and to
calculate antenna weights for the antenna elements using one of an
error minimizing algorithm and an adaptive metric optimization
algorithm.
22. The repeater of claim 21, wherein the one or more reference
signals comprise one or more pilot code phases of a CDMA-based
communication system.
23. The repeater of claim 21, wherein the one or more reference
signals comprise one or more scrambling codes of a WCDMA-based
communication system.
24. The repeater of claim 21, wherein the one or more reference
signals comprise one or more pilot tones of an OFDM symbol or an
OFDM preamble.
25. The repeater of claim 21, wherein the receive signals include
the feedback signals of the repeater and the antenna weight
computation module is configured to select a desired receive signal
being a receive signal with the largest correlated energy level a
given delay prior to the receive signal with the overall largest
correlated power level, the receive signal with the overall largest
correlated power being a feedback signal and the given delay being
a delay through the repeater.
26. The repeater of claim 21, wherein the antenna weight
computation module is configured to calculate antenna weights in
closed form using error minimizing algorithm to minimize an error
between the desired receive signal and the reference signal.
27. The repeater of claim 21, wherein the antenna weight
computation module is configured to calculate antenna weights in
closed form using a minimum mean square error (MMSE) algorithm to
minimize a mean square error between the desired receive signal and
the reference signal.
28. The repeater of claim 21, wherein the antenna weight
computation module is configured to calculate antenna weights
adaptively for the selected antenna elements to maximize a
signal-to-noise ratio (SNR) of the desired receive signal.
29. The repeater of claim 28, wherein the antenna weight
computation module is configured to calculate antenna weights
recursively using a metric and an adaptive metric optimization
algorithm to optimize the metric, the metric being indicative of
the SNR of the desired receive signal.
30. The repeater of claim 29, wherein the metric comprises a ratio
of the correlated power measurement of the desired receive signal
to the sum of the correlated power measurements of some or all of
the other receive signals.
31. The repeater of claim 30, wherein the metric comprises a ratio
of the correlated power measurement of the desired receive signal
to the sum of the correlated power measurements of dominant
non-desired receive signals, the dominant non-desired receive
signals being the receive signals other than the desired receive
signal having a correlated power level above a predetermined
threshold.
32. The repeater of claim 29, wherein the adaptive metric
optimization algorithm comprises a steepest descent adaptive
algorithm applied to modify the antenna weights of M antenna
elements to optimize the metric.
33. The repeater of claim 20, further comprising an echo canceller
configured to cancel estimated feedback signals from the receive
signals.
34. The repeater of claim 33, wherein the antenna weight
computation module is further configured to combine the weighted
receive signals and amplify and transmit the combined signals as
output signals on the antenna array of the repeater.
35. The repeater of claim 20, wherein the antenna weight
computation module is further configured to combine the weighted
receive signals, cancel estimated feedback signals from the
combined signals, and amplify and transmit the echo cancelled
signals as output signals on the antenna array of the repeater.
36. The repeater of claim 20, wherein the antenna element selection
module is configured to select at least one antenna element of the
vertical feed mode and one antenna element of the horizontal feed
mode for each combination of antenna elements.
37. The repeater of claim 20, wherein the antenna element selection
module is configured to determine a performance result associated
with each selected combination of antenna elements based on one or
more performance factors, the one or more performance factors
including one of an amount of feedback signal, a channel quality
and a signal-to-noise ratio (SNR) of the receive signal.
38. The repeater of claim 37, wherein the antenna element selection
module is configured to select a combination of antenna elements
from the first and second antenna arrays to optimize a desired
performance result based on a combination of antenna elements
having a lowest feedback signal, or a combination of antenna
elements providing a channel with a high degree of ease of feedback
cancellation, or a combination of antenna elements providing a
highest signal-to-noise ratio (SNR) of the receive signal.
39. The repeater of claim 37, wherein the antenna element selection
module is configured to determine a performance result associated
with each selected combination of antenna elements based on a
weighted sum of one or more performance factors.
40. A computer readable medium having stored thereon computer
executable instructions for performing at least the following acts:
(a) selecting a combination of antenna elements from first and
second antenna arrays of an echo cancellation repeater, each
antenna array including a first set of antenna elements for
vertical feed mode and a second set of antenna elements for
horizontal feed mode; (b) receiving incoming receive signals on
receiver circuits associated with the selected antenna elements;
(c) generating correlation energy measurements indicative of
correlation of the receive signals and one or more reference
signals; (d) selecting a desired receive signal being a receive
signal with the largest correlated energy level, excluding receive
signals that are feedback signals; (e) calculating antenna weights
for the selected antenna elements using one of an error minimizing
algorithm and an adaptive metric optimization algorithm; (f)
determining a performance result associated with the selected
combination of antenna elements; (g) storing calculated antenna
weights and the performance result associated with the selected
combination of antenna elements; (h) repeating steps (a) to (g) for
one or more combinations of antenna elements from the first and
second antenna arrays; and (i) selecting a combination of antenna
elements from the first and second antenna arrays based on the
stored performance results.
41. A repeater for a wireless communication network, the repeater
employing echo cancellation and employing a first antenna array and
a second antenna array, each antenna array including a first set of
antenna elements for vertical feed mode and a second set of antenna
elements for horizontal feed mode, the repeater comprising: means
coupled to each set of two or more antenna elements in each of the
first and second antenna arrays, the means for selecting one of the
two or more antenna elements coupled thereto; means for receiving
incoming receive signals associated with the selected antenna
elements; means for selecting one or more combinations of antenna
elements, performing calculations of antenna weights for each
selected combination of antenna elements, determining a performance
result associated with each selected combination of antenna
elements, and selecting a combination of antenna elements from the
first and second antenna arrays based on the performance results;
and means for applying the calculated antenna weight to condition
the receive signals.
42. A method to reduce interference in an echo cancellation
repeater for a wireless communication network, the repeater
employing a first antenna array and a second antenna array, each
antenna array including a first set of antenna elements for
vertical feed mode and a second set of antenna elements for
horizontal feed mode, the method comprising: (a) receiving incoming
receive signals on receiver circuits associated with the antenna
elements; (b) generating correlation energy measurements indicative
of correlation of the receive signals and one or more reference
signals; (c) selecting a desired receive signal being a receive
signal with the largest correlated energy level, excluding receive
signals that are feedback signals of the repeater; (d) calculating
antenna weights for the antenna elements using one of an error
minimizing algorithm and an adaptive metric optimization algorithm;
(e) determining a performance result associated with the antenna
elements; (f) performing beamforming in baseband to adjust the
calculated antenna weights, the adjusted antenna weights selecting
a combination of antenna elements from the first and second antenna
arrays for receiving and transmitting signals; and (g) performing
echo cancellation on the receive signal or on a weighted combined
receive signal using the calculated antenna weights.
43. The method of claim 42, wherein determining a performance
result associated with the antenna elements comprises: determining
the performance result based on one or more performance factors,
the one or more performance factors including one of an amount of
feedback signal, a channel quality and a signal-to-noise ratio
(SNR) of the receive signal.
44. The method of claim 43, wherein performing beamforming in
baseband to adjust the calculated antenna weights to optimize a
desired performance result comprises: performing beamforming in
baseband to adjust the calculated antenna weights to optimize a
desired performance result based on a combination of antenna
elements having the lowest feedback signal, or a combination of
antenna elements providing a channel with a high degree of ease of
feedback cancellation, or a combination of antenna elements
providing a highest signal-to-noise ratio (SNR) of the receive
signal.
45. The method of claim 43, wherein determining the performance
result based on one or more performance factors comprises
determining the performance result based on a weighted sum of one
or more performance factors.
46. A repeater for a wireless communication network, the repeater
employing echo cancellation and employing a first antenna array and
a second antenna array, each antenna array including a first set of
antenna elements for vertical feed mode and a second set of antenna
elements for horizontal feed mode, the repeater comprising:
receiver circuits coupled to receive incoming receive signals
associated with the antenna elements; an antenna element selection
module and an antenna weight computation module configured to
perform calculations of antenna weights for the antenna elements,
to determine a performance result associated with the antenna
elements, and to select a combination of antenna elements from the
first and second antenna arrays based on the performance results;
an antenna weight application module configured to apply the
calculated antenna weight to condition the receive signals; and an
echo canceller configured to cancel estimated feedback signals from
the receive signals or from a weighted combined receive signal
using the calculated antenna weights.
47. The repeater of claim 46, wherein the antenna element selection
module is configured to determine a performance result associated
with the antenna elements based on one or more performance factors,
the one or more performance factors including one of an amount of
feedback signal, a channel quality and a signal-to-noise ratio
(SNR) of the receive signal.
48. The repeater of claim 47, wherein the antenna element selection
module is configured to select a combination of antenna elements
from the first and second antenna arrays based on a combination of
antenna elements having the lowest feedback signal, or a
combination of antenna elements providing a channel with a high
degree of ease of feedback cancellation, or a combination of
antenna elements providing a highest signal-to-noise ratio (SNR) of
the receive signal.
49. The repeater of claim 47, wherein the antenna element selection
module is configured to determine a performance result associated
with each selected combination of antenna elements based on a
weighted sum of one or more performance factors.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of application
Ser. No. 12/836,493, filed Jul. 14, 2010, entitled "Method In a
Wireless Repeater Employing an Antenna Array for Interference
Reduction," having at least one common inventor, which patent
application is incorporated herein by reference in its
entirety.
BACKGROUND
[0002] 1. Field
[0003] This disclosure generally relates to repeaters in wireless
communication systems.
[0004] 2. Background
[0005] Wireless communication systems and techniques have become an
important part of the way we communicate. However, providing
coverage can be a significant challenge to wireless service
providers. One way to extend coverage is to deploy repeaters. In
general, a repeater is a device that receives a signal, amplifies
the signal, and transmits the amplified signal. A typical repeater
configuration includes a donor antenna as an example network
interface to network infrastructure such as a base station. The
repeater also includes a server antenna (also referred to as a
"coverage antenna") as a mobile interface to one or more mobile
devices. In operation, the donor antenna is in communication with
the base station, while the server antenna is in communication with
one or more mobile devices. Signals from the base station are
amplified using forward link circuitry, while signals from the
mobile devices are amplified using reverse link circuitry. Many
configurations may be used for the forward link circuitry and the
reverse link circuitry.
[0006] There are many types of repeaters. In some repeaters, both
the network and mobile interfaces are wireless; while in others, a
wired network interface is used. Some repeaters receive signals
with a first carrier frequency and transmit amplified signals with
a second different carrier frequency, while others receive and
transmit signals using the same carrier frequency. For "same
frequency" repeaters, one particular challenge is managing the
feedback that occurs since some of the transmitted signal can leak
back to the receive circuitry and be amplified and transmitted
again. Existing repeaters manage feedback using a number of
techniques, including physical isolation between the donor and
server antennae and echo cancellation techniques.
[0007] Wireless service providers continue to face issues such as
inadequate indoor 3G voice and data coverage, especially in homes
and SOHOs (Small Offices, Home Offices). Repeaters have a long
history in wireless networks, with mixed results. Very large
infrastructure related repeaters have been successfully deployed to
fill coverage holes and reduce total base station sites during
initial deployments. However, personal repeaters (indoor self
installation type) have not been successfully adopted broadly in
the market due to a number of factors. One issue which impacts the
deployments of personal repeaters in congested areas is "pilot
pollution", or other interfering signals. Pilot pollution is the
situation when too many base stations are received at the mobile or
the repeater's receiver causing a reduction in signal quality.
While many 3G systems use soft hand off, there are limits to when
the soft hand off approach provides benefit, and when too many
signals are simply interference. Further, for data optimized
systems, such as 1XEV-DO, and 4G systems, such as LTE, soft handoff
is often not used, opting rather for a fast selection diversity
between base stations.
[0008] The interfering condition of too many signals at a receiver
is especially problematic for "same frequency" repeaters because
boosting the signal may simply amplify and broadcast a poor
signal-to-noise ratio (SNR) signal which may not be beneficial in
some cases. Generally a repeater cannot improve the quality of the
signal it receives and in the condition of strong signal level, but
significant interference, a repeater may not provide significant
benefit because the repeater would only cause an increase in the
interfering noise of the system.
SUMMARY
[0009] Systems, apparatuses, and methods disclosed herein allow for
enhanced repeater capability. In one embodiment, a method to reduce
interference in an echo cancellation repeater for a wireless
communication network where the repeater employs a first antenna
array and a second antenna array and each antenna array includes a
first set of antenna elements for vertical feed mode and a second
set of antenna elements for horizontal feed mode includes: (a)
selecting a combination of antenna elements from the first and
second antenna arrays; (b) receiving incoming signals on receiver
circuits associated with the selected antenna elements; (c)
generating correlation energy measurements indicative of the
correlation of the receive signals and one or more reference
signals; (d) selecting a desired receive signal being a receive
signal with the largest correlated energy level, excluding receive
signals that are feedback signals of the repeater; (e) calculating
antenna weights for the selected antenna elements using one of an
error minimizing algorithm and an adaptive metric optimization
algorithm; (f) determining a performance result associated with the
selected combination of antenna elements; (g) storing calculated
antenna weights and the performance result associated with the
selected combination of antenna elements; (h) repeating steps (a)
to (g) for one or more combinations of antenna elements from the
first and second antenna arrays; and (i) selecting a combination of
antenna elements from the first and second antenna arrays based on
the stored performance results. The combination of antenna elements
may be selected to optimize a desired performance result.
[0010] According to another aspect of the present invention, a
repeater for a wireless communication network where the repeater
employs echo cancellation and employs a first antenna array and a
second antenna array and each antenna array includes a first set of
antenna elements for vertical feed mode and a second set of antenna
elements for horizontal feed mode includes: one or more switches
where each switch is coupled to two or more antenna elements in
each of the first and second antenna array and the one or more
switches is configured to select one of the two or more antenna
elements coupled thereto; receiver circuits coupled to the one or
more switches to receive incoming signals associated with the
selected antenna elements; an antenna element selection module and
an antenna weight computation module configured to select one or
more combinations of antenna elements, to perform calculations of
antenna weights for each selected combination of antenna elements,
to determine a performance result associated with each selected
combination of antenna elements, and to select a combination of
antenna elements from the first and second antenna arrays based on
the performance results; and an antenna weight application module
configured to apply the calculated antenna weight to condition the
receive signals.
[0011] According to yet another aspect of the present invention, a
method to reduce interference in an echo cancellation repeater for
a wireless communication network where the repeater employs a first
antenna array and a second antenna array and each antenna array
includes a first set of antenna elements for vertical feed mode and
a second set of antenna elements for horizontal feed mode includes:
(a) receiving incoming signals on receiver circuits associated with
the antenna elements; (b) generating correlation energy
measurements indicative of the correlation of the receive signals
and one or more reference signals; (c) selecting a desired receive
signal being a receive signal with the largest correlated energy
level, excluding receive signals that are feedback signals of the
repeater; (d) calculating antenna weights for the antenna elements
using one of an error minimizing algorithm and an adaptive metric
optimization algorithm; (e) determining a performance result
associated with the antenna elements; (f) performing beamforming in
baseband to adjust the calculated antenna weights, the adjusted
antenna weights selecting a combination of antenna elements from
the first and second antenna arrays for receiving and transmitting
signals.
[0012] According to yet another aspect of the present invention, a
repeater for a wireless communication network where the repeater
employs echo cancellation and employs a first antenna array and a
second antenna array and each antenna array includes a first set of
antenna elements for vertical feed mode and a second set of antenna
elements for horizontal feed mode includes: receiver circuits
coupled to receive incoming signals associated with the antenna
elements; an antenna element selection module and an antenna weight
computation module configured to perform calculations of antenna
weights for the antenna elements, to determine a performance result
associated with the antenna elements, and to select a combination
of antenna elements from the first and second antenna arrays based
on the performance results; and an antenna weight application
module configured to apply the calculated antenna weight to
condition the receive signals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a block diagram of exemplary repeater components
in accordance with the systems and methods described herein.
[0014] FIG. 2 shows a diagram of an operating environment for a
repeater according to embodiments of the present invention.
[0015] FIG. 3 illustrates an exemplary repeater operative to
perform signal conditioning and amplification using one or more
antenna arrays according to embodiments of the present
invention.
[0016] FIG. 4 illustrates a repeater environment in which a
repeater with an antenna array is deployed according to embodiments
of the present invention.
[0017] FIG. 5 illustrates an operating environment in which a
wireless repeater with an antenna array is deployed.
[0018] FIG. 6 is a flow chart illustrating an adaptive antenna
weight computation method in a repeater employing an antenna array
for improving signal reception according to one embodiment of the
present invention.
[0019] FIG. 7 illustrates the correlation results obtained for the
repeater in the operating environment of FIG. 5.
[0020] FIG. 8 illustrates the correlated power computed for
incoming signals received at a repeater employing an antenna array
in an operating environment including multiple signal sources, such
as multiple base stations according to one embodiment of the
present invention.
[0021] FIG. 9 illustrates the correlated power computed for
incoming signals received at a repeater employing an antenna array
in an operating environment including multiple signal sources, such
as multiple base stations according to another embodiment of the
present invention.
[0022] FIG. 10 is a schematic diagram of a repeater employing an
antenna array and employing echo cancellation after the antenna
weights are determined according to one embodiment of the present
invention.
[0023] FIG. 11 is a flowchart illustrating an adaptive antenna
weight computation method implemented in the repeater of FIG. 10
using closed form MMSE algorithm according to one embodiment of the
present invention.
[0024] FIG. 12 is a schematic diagram of a repeater employing an
antenna array and employing echo cancellation before the antenna
weights are determined according to one embodiment of the present
invention.
[0025] FIG. 13 is a flowchart illustrating an adaptive antenna
weight computation method implemented in the repeater of FIG. 12
using closed form MMSE algorithm according to one embodiment of the
present invention.
[0026] FIG. 14 is a schematic diagram of a repeater employing an
antenna array and employing echo cancellation after the antenna
weights are determined according to one embodiment of the present
invention.
[0027] FIG. 15 is a flowchart illustrating an adaptive antenna
weight computation method implemented in the repeater of FIG. 14
using a metric with a metric optimization algorithm according to
one embodiment of the present invention.
[0028] FIG. 16 is a schematic diagram of a repeater employing an
antenna array and employing echo cancellation before the antenna
weights are determined according to one embodiment of the present
invention.
[0029] FIG. 17 is a flowchart illustrating an adaptive antenna
weight computation method implemented in the repeater of FIG. 16
using a metric with a metric optimization algorithm according to
one embodiment of the present invention.
[0030] FIG. 18 illustrates an echo cancellation repeater operative
to perform signal conditioning and amplification using one or more
antenna arrays according to embodiments of the present
invention.
[0031] FIG. 19 is a flow chart illustrating an antenna element
selection method incorporating the antenna weight computation
method implemented in an echo cancellation repeater employing
antenna arrays for improving signal reception according to one
embodiment of the present invention.
[0032] FIG. 20 illustrates an echo cancellation repeater operative
to perform signal conditioning and amplification using one or more
antenna arrays according to embodiments of the present
invention.
[0033] FIG. 21 is a flow chart illustrating an antenna element
selection method incorporating the antenna weight computation
method implemented in an echo cancellation repeater employing
antenna arrays for improving signal reception according to one
embodiment of the present invention.
DETAILED DESCRIPTION
[0034] The nature, objectives, and advantages of the disclosed
method and apparatus will become more apparent to those skilled in
the art after considering the following detailed description in
connection with the accompanying drawings.
Repeater with Antenna Array
[0035] A repeater incorporating an antenna array and an echo
cancellation module and utilizing a composite metric for optimizing
the weight settings for the antenna array for enhancing echo
cancellation is described in copending and commonly assigned U.S.
Patent Application Publication No. 2008/0225931, entitled "Use of
Adaptive Antenna Array in conjunction with an ON-Channel Repeater
to improve signal quality," by J. Proctor et al, filed Mar. 3, 2008
and published Sep. 18, 2008, which patent application is
incorporated herein by reference in its entirety. The composite
metric is derived from other metrics available in the repeater
system and can include Ec/Io, SNR, RSSI, Correlated Power and
specific isolation related metrics associated with the repeater
operation. For instance, by combining the residual leakage metric
with other metrics, cancellation and array weights can be jointly
optimized.
[0036] FIG. 1 duplicates FIG. 4 of the '931 patent application and
is a block diagram of exemplary repeater components in accordance
with the systems and methods described herein. More specifically,
FIG. 1 illustrates one side of an antenna configuration for use in
providing selected isolation for an exemplary repeater. Antenna
configuration 400 comprises PCB board 405 having one or more patch
antennas 410 and 415 mounted thereto. Note that typically there
would be a like number of antenna patches on the opposite side of
PCB and typically orientated in an opposite or advantageous
polarization when compared to the polarization of antennas 410 and
415, such that a sufficient or even maximum amount of isolation is
achieved between the antennas on opposite sides of the PCB. In an
illustrative implementation, PCB board 405 can comprise one or more
patch antennas 410 and 415 in various configurations and have more
than one pair of patch antennas as well as an uneven number of
respective patch antennas that make up a superset thereof. Antenna
configuration 400 can, with the deployment of patch antennas 410
and 415 along with a like number of antenna on the opposite side of
the PCB, provide selected isolation between a transmit and receive
channel (e.g., transmit channels operatively coupled to one or more
patch antennae and receive channels operatively coupled to one or
more patch antennae) to cooperate with isolation and amplification
provided by an exemplary cooperating feedback cancellation loop
(e.g., feedback cancellation loop operatively coupled to an antenna
array). The configuration of FIG. 1 shows one example of antenna
arrays that can be used in embodiments described herein.
[0037] FIG. 2 shows a diagram of an operating environment 200 for a
repeater 210 according to embodiments of the present invention. The
example of FIG. 2 illustrates forward link transmissions; i.e., a
remote signal 140 from a base station 225 is intended for a mobile
device 230. A repeater, such as repeater 210, may be used in
environment 200 if an un-repeated signal along the path 227 between
base station 225 and mobile device 230 would not provide sufficient
signal for effective voice and/or data communications received at
mobile device 230. Repeater 210 with a gain G and a delay .DELTA.
is configured to repeat a signal received from base station 225 on
a donor antenna 215 to mobile device 230 using a server antenna
220. The donor antenna is also referred to as "the receiving
antenna" for the example of a forward link transmission while the
server antenna is also referred to as "the transmitting antenna"
for forward link transmissions. Repeater 210 includes forward link
circuitry for amplifying and transmitting signals received from the
base station 225 to mobile device 230 through donor antenna 215 and
server antenna 220. Repeater 210 may also include reverse link
circuitry for amplifying and transmitting signals from mobile
device 230 back to base station 225. At repeater 210, the remote
signal s(t) is received as an input signal and the remote signal
s(t) is repeated as a repeated or amplified signal y(t) where y(t)=
{square root over (G)}s(t-.DELTA.).
[0038] Ideally, the gain G of a repeater would be made as large as
possible. In practice, the gain of repeater 210 is limited by the
isolation between donor antenna 215 and server antenna 220. If the
gain is too large, the repeater can become unstable due to signal
leakage. Signal leakage refers to the phenomenon where a portion of
the signal that is transmitted from one antenna (in FIG. 2, server
antenna 220) is received by the other antenna (in FIG. 2, donor
antenna 215), as shown by the feedback path 222 in FIG. 2. Without
interference cancellation or other techniques, the repeater would
amplify this feedback signal, also referred to as the "leakage
signal," as part of its normal operation, and the amplified
feedback signal would again be transmitted by server antenna 220.
The repeated transmission of the amplified feedback signal due to
signal leakage and high repeater gain can lead to repeater
instability. In general, repeaters may employ interference
cancellation or echo cancellation to reduce or eliminate the amount
of leakage signal between the repeater's antennas, thereby
improving the antenna isolation. Herein, "interference
cancellation" or "echo cancellation" refers to cancellation of an
estimated leakage signal, which provides for partial or complete
cancellation of the actual leakage signal.
[0039] FIG. 3 illustrates an exemplary repeater 500 operative to
perform signal conditioning and amplification using one or more
antenna arrays according to embodiments of the present invention.
Repeater 500 includes a first antenna array 505 having antenna
elements 510 and 515, a second antenna array having antenna
elements 530 and 535, a processing circuitry 545 including a
multiple transceiver circuit 520 and a controller 525. The antenna
arrays 505 and 540 can cooperate with multiple transceiver circuit
520 which cooperates with controller 525 as part of operations of
repeater 500. Signals can be received by antenna arrays 505 and 540
and passed to processing circuitry 545 for signal conditioning and
processing and then passed back to antenna arrays 505 and 540 for
communication with one or more cooperating components (e.g., base
station of a CDMA wireless communications network).
[0040] In other embodiments, antenna arrays 505 and 540 can include
additional antenna elements as desired. Further, the number and
configuration of the antenna arrays described herein are merely
illustrative as the herein described repeater systems and methods
contemplate use of varying number of antenna arrays having varying
configurations and comprising varying number of antenna
elements.
[0041] FIG. 4 illustrates a repeater environment in which a
repeater with an antenna array is deployed according to embodiments
of the present invention. A repeater 620 in repeater environment
600 includes an antenna array 645 having a first antenna 625 and a
fourth antenna 640, a multiple transceiver element 630, and an
antenna array 650 comprising a second antenna element 660 and a
third antenna element 655. Operatively, downlink signals 610
originating from first network 605 can be processed by repeater 620
to generate repeated downlink signals 665 for communication to
second network 675, and uplink signals originating from second
network 675 can be processed by repeater 620 to generate repeated
uplink signals 615 for communication to first network 605.
Configuration and orientation of the antenna arrays 645 and 650
promote selected isolation of the unconditioned uplink and downlink
signals and promote desired amplification and gain of such
signals.
[0042] In other embodiments, repeater 620 can include additional
antenna elements. Further, it is appreciated that the number and
configuration of the antenna arrays described herein are merely
illustrative as the repeater system and method of the present
invention contemplate use of varying number of antenna arrays
having varying configurations and comprising varying number of
antenna elements.
Array Weight Determination for Interference Reduction
[0043] Systems and techniques herein provide for repeaters with an
antenna array employing spatial selectivity to improve the quality
of the signal the repeater receives. In general, a conventional
repeater cannot improve the quality of the signal it receives, only
amplifying what is receives. In embodiments of the present
invention, the repeaters implementing the systems and techniques of
the present invention use adaptive metric optimization algorithms
or error minimizing algorithms to determine the array weights so as
to steer reception of the antenna array, thereby improving the
quality of the receive signal, improving reception and removing
interferences.
[0044] In some embodiments, systems and techniques herein provide
for a wireless repeater employing an antenna array whereby a
desired receive signal is selected through correlation with a
reference signal. In CDMA based communication systems, the
reference signal is the known pilot signal or the known pilot code.
More specifically, the pilot code can be the pilot channel or pilot
code phase transmitted by the base stations in a CDMA communication
system, or the pilot code can be the scrambling code in a WCDMA
communication system. In non-CDMA based communication system, the
reference signal can be some or all of the pilot tones in an OFDM
symbol or an OFDM preamble.
[0045] In some embodiments, the array weights for the antenna array
are determined adaptively by maximizing the signal-to-noise ratio
(SNR) of the desired receive signal. More specifically, in one
embodiment, the antenna weights are adapted using a metric and an
adaptive metric optimization algorithm. That is, a metric is
provided to estimate the SNR of the desired receive signal and the
antenna weights are recursively computed to optimize the
predetermined metric. Examples of adaptive metric optimization
algorithms include steepest decent based algorithms. In one
embodiment, the metric used is the ratio of the correlated power of
the desired receive signal to the sum of the correlated power of
all or some of the other receive signals. Furthermore, in one
embodiment, a steepest descent algorithm is used to recursively
determine the antenna weights while optimizing the aforementioned
metric.
[0046] In other embodiments, the antenna weights are computed using
closed form calculations using an error minimizing algorithm, such
as using a minimum mean square error (MMSE) algorithm or a
least-mean square (LMS) algorithm. In one embodiment, the antenna
weights are determined in closed form to minimize the mean square
error between the receive signal and the reference signal.
[0047] FIG. 5 illustrates an operating environment 750 in which a
wireless repeater with an antenna array is deployed. A wireless
repeater 756 may be positioned in the coverage area of two or more
base stations 752, 754. In most cellular communication systems,
such as GSM, UMTA or CDMA, the base stations transmit a reference
signal or a pilot signal that is unique to each base station. For
example, in CDMA based communication systems, a pilot signal is an
unmodulated, direct-sequence spread spectrum signal transmitted
continuously by each CDMA base station. The pilot signal is
comprised of a pseudo-random code (the "pilot code"), also referred
to as pseudo-noise (PN). The pilot code is sometimes referred to as
a "spreading code" being the code used to spread the bandwidth of
the signal to be transmitted and is independent of the data. More
specifically, in a cellular communication system, the base stations
transmit the same PN code but each base station is assigned with a
different offset to allow mobile devices to identify the base
station by the PN code offset. In the present description, the
reference signal or unique pilot signal refers to the pilot signal
transmitted with each base station having the same PN code but with
a different code offset. In the present illustration, base station
752 transmits a pilot signal with a pseudo-random code PN1 while
base station 754 transmits a pilot signal with a pseudo-random code
PN2. In the present illustration, pilot codes PN1 and PN2 represent
the same pseudo-random code but at different offset or different
phase shift.
[0048] The pilot signals are typically transmitted at a constant
power level to provide a fixed reference for receivers within its
coverage area, such as mobile stations or repeaters. A receiver,
such as a mobile station or a repeater, listens to the pilot
signals of the base stations to search for a base station with the
strongest correlated power level. In a normal communication
environment, the pilot signal is used by the receivers for various
connection operations, such as to acquire the timing of the CDMA
link, to provide a phase reference, and to determine the signal
strength.
[0049] A wireless repeater deployed in a cellular system has the
capability to communicate with multiple base stations. However,
when there are too many pilot signals observed in an area, pilot
pollution occurs. Hearing unnecessary pilot signals reduce the
received energy per chip over the power density (E.sub.C/I.sub.0)
from the intended base station, consequently reducing the quality
of the desired connection. For instance, as shown in FIG. 5,
repeater 756 is within the coverage area of both base station 752
and base station 754. If base station 752 is the intended base
station for repeater 756, then the pilot signal transmitted by base
station 754 becomes interference to repeater 756, degrading the
quality of the signal received by repeater 756 from base station
752.
[0050] According to one aspect of the present invention, repeater
756 employs an antenna array and implements the antenna weight
computation method of the present invention to reduce interference
due to pilot pollution and improve signal reception. More
specifically, repeater 756 applies the antenna weight computation
method of the present invention to modify the spatial selectivity
of the antenna array so as to steer the antenna array of the
repeater to be more receptive to transmission from one base station
(such as base station 752) over transmission from other surrounding
base stations (such as base station 754), thereby improving the
quality of the receive signals from the intended base station.
[0051] In an antenna array, the signal from each antenna element
can be multiplied by a different weight to achieve the desired
antenna spatial selectivity. In the present description, array
weights refer to the complex values (e.g. W=a+jb) used to multiply
the receive signal of each antenna element. The weighted receive
signals of all the antenna elements are combined to form the
antenna beam. When the array weights are chosen properly, the
antenna beam can be steered in such a way so as to cancel energy
from undesirable directions and emphasis energy from desired
directions. That is, the antenna beam can be steered by changing
the antenna weights to change the direction of maximum
reception.
[0052] FIG. 6 is a flow chart illustrating an antenna weight
computation method implemented in a repeater employing an antenna
array for improving signal reception according to one embodiment of
the present invention. Referring to FIG. 6, antenna weight
computation method 700 is implemented in a repeater employing an
antenna array including M antenna elements. Each of the M antenna
elements is coupled to a transceiver circuit of the repeater to
process incoming and outgoing signals. More specifically, each
transceiver circuit includes a receiver circuit to receive the
incoming receive signal from the associated antenna element and a
transmitter circuit to provide the outgoing transmitted signal to
the associated antenna element. At step 702, the repeater receives
incoming signals from the operating environment on M receiver
circuits associated with M antenna elements of the antenna array.
The incoming signals can include remote signals from nearby base
stations and the feedback signal from the repeater's own
antennas.
[0053] Method 700 performs correlation of the receive signals with
one or more reference signals (step 704). When the repeater is
deployed in a CDMA based communication system, the reference
signals are the known pilot signals or known pilot codes or known
pilot code phases of the base stations in the system. Pilot code
phases refer to the same pilot code with known code offsets. When
the repeater is deployed in a WCDMA based communication system, the
reference signals are the known scrambling codes of the base
stations in the system. Finally, when the repeater is deployed in a
non-CDMA based communication system, the reference signals are some
or all of the pilot tones in an OFDM symbol or an OFDM preamble. In
other communication systems, the known pilot codes or pilot signals
used in those systems can be used as the reference signals. Method
700 computes the correlated power or correlated energy of the
receive signals corresponding to the one or more reference signals,
such as one or more pilot codes or pilot tones.
[0054] From the correlation results, method 700 selects a desired
receive signal being the receive signal, other than the feedback
signal, having the largest correlated power with a reference
signal, such as a known pilot code phase (step 706). That is, the
desired receive signal is selected from the receive signals
excluding the leakage or feedback signals at the repeater, if any.
It is instructive to note that in some repeaters, the antenna
weights are determined after echo cancellation is carried out,
while in other repeaters, the antenna weights are determined before
echo cancellation or without echo cancellation. In the case when
antenna weights are determined before or without echo cancellation,
the largest correlated power detected by method 700 could be the
feedback signal from the repeater itself. Any leakage or feedback
signals should be excluded when selecting the desired receive
signal. Accordingly, in one embodiment, the desired receive signal
is determined by searching for the signal with the largest
correlated power a delay D prior to the signal with the overall
largest correlated power level, the signal with the overall largest
correlated power being the feedback signal, where delay D
represents the delay through the repeater.
[0055] FIG. 7 illustrates the correlation results obtained for the
repeater 756 in operating environment 750 of FIG. 5. Referring to
FIG. 7, repeater 756 receives incoming signals from base stations
752 and 754. The correlation of a first receive signal with pilot
code PN1 gives a correlated energy level denoted by line 760A while
the correlation of a second receive signal with pilot code PN2
gives a correlated energy level denoted by line 762A. The
correlated energy 760A is greater than the correlated energy 762A.
Thus, the first receive signal corresponding to pilot code PN1 will
be selected as the desired receive signal.
[0056] Once the desired receive signal is selected, method 700
determines the weights to be used with each of the M antenna
elements (the "array weights") in order to steer the antenna beam
for improving spatial selectivity. The array weights can be
determined using various algorithms and metrics.
[0057] In some embodiments, the array weights are determined by
minimizing the error between the desired receive signal and the
reference signal (step 708). More specifically, in some
embodiments, the array weights are calculated in closed form using
an error minimizing algorithm (step 710). In one embodiment, closed
form calculation using a minimum mean square error (MMSE) algorithm
is used to determine the array weights. More specifically, the
antenna weights are computed in closed form to minimize the mean
square error between the desired receive signal and the reference
signal (the known pilot signal or pilot code phase). The MMSE
algorithm is applied to select antenna weights so that the desired
receive signal looks as close as possible to the reference signal
in phase and in magnitude. For example, in the operating
environment 750 (FIG. 5), the array weights are calculated in
closed form to minimize the mean square error between the desired
receive signal at repeater 756 and the pilot signal containing
pilot code phase PN1. In other embodiments, other closed form
algorithm can be used to compute the array weights.
[0058] In alternate embodiments, the array weights are determined
adaptively to maximize the signal-to-noise ratio (SNR) of the
desired receive signal (step 712). In some embodiments, the array
weights are computed recursively using a metric and an adaptive
metric optimization algorithm (step 714). That is, a metric is
provided to estimate the SNR of the desired receive signal and the
antenna weights are recursively computed to optimize the
predetermined metric. In some embodiments, the metric used is the
ratio of the correlated power of the desired receive signal to the
sum of the correlated power of some or all of the other receive
signals. In one embodiment, the metric sums only the dominant
non-desired receive signals as the denominator of the ratio where
the dominant non-desired receive signals refer to receive signals
other than the desired receive signal having a correlated power
level above a predetermined threshold. Furthermore, in one
embodiment, a steepest descent algorithm is used to recursively
determine the antenna weights while optimizing the metric. The
construction of the metric to be used will be described in more
detail below. The use of a steepest descent algorithm is
illustrative only. In other embodiments, other adaptive metric
optimization algorithm can be used.
[0059] It is imperative to note that the error minimizing
computation method (steps 708-710) and the SNR maximizing
computation method (steps 712-714) represent alternate methods for
determining the array weights of the antenna array. They are both
shown in the flowchart of FIG. 7 to illustrate the alternate
methods but method 700 can be implemented with one or the other
array weight computation method and does not need to implement both
array weight computation methods at the same time.
[0060] As a result of the antenna weight computation method, the
antenna array of the repeater is steered to maximize reception in
the direction of the desired receive signal and minimize reception
from the interfering non-desired signals. In this manner,
interference from neighboring cells is reduced. For instance, in
the repeater environment 750 of FIG. 5, the antenna array of
repeater 756 is steered to be more selective to the signals from
base station 752 and less selective to signals from base station
754. In operation, antenna weight computation method 700 has the
effect of increasing the correlated energy of the desired receive
signal with pilot code PN1 while suppressing or reducing the
correlated energy of the other receive signals, such as the second
receive signal with pilot code PN2. Thus, referring to FIG. 7, as a
result of the antenna weight computation, the correlated energy of
the desired receive signal is increased to a level denoted by line
760B while the correlated energy of the non-desired receive signal
is decreased to a level denoted by line 762B. In this manner, the
SNR of the desired receive signal is improved.
Array Weight Computation Using Adaptive Metric Optimization
[0061] The use of a metric and an adaptive metric optimization
algorithm in the adaptive antenna weight computation method of the
present invention will now be described in more detail. In
embodiments of the antenna weight computation method of the present
invention, an adaptive metric optimization algorithm is applied to
compute the antenna weights recursively with the goal of optimizing
a predetermined metric. In embodiments of the present invention,
the metric being applied is a metric that estimates the SNR of the
desired receive signal and the metric is optimized to maximize the
SNR. In one embodiment, the metric being optimized is given as the
ratio of the correlated power of the desired receive signal to the
sum of the correlated power of some or all of the other receive
signals. The derivation of the metric is illustrated in FIG. 8 for
the case where the array weights are determined after
echo-cancellation and in FIG. 9 for the case where the array
weights are determined before echo-cancellation.
[0062] FIG. 8 illustrates the correlated power computed for
incoming signals received at a repeater employing an antenna array
in an operating environment including multiple signal sources, such
as multiple base stations, according to one embodiment of the
present invention. In the present illustration, the repeater is
assumed to implement echo cancellation and the incoming feedback
signals have been echo cancelled before the array weights are to be
determined Referring to FIG. 8, the repeater receives five incoming
signals corresponding to pilot signals with five pilot codes or
pilot signals with five different PN code offsets of a PN code
sequence. The five receive signals with the corresponding pilot
codes or pilot code offsets are denoted by reference numerals A to
E. In one embodiment, a metric for antenna weight adaptation is
constructed by using the correlated power of the desired receive
signal as the numerator. In the present illustration, the desired
receive signal is signal A, being the signal with the largest
correlated power. More specifically, in one embodiment, the
absolute value of the correlated power of the desired receive
signal is taken and is squared to use as the numerator of the
metric.
[0063] In one embodiment, the metric for antenna weight adaptation
is constructed using the sum of the correlated power of all other
receive signals as the denominator. That is, the sum of the
correlated power of signals B to E is used as the denominator of
the metric. In another embodiment, an enhanced metric is provided
where the metric is constructed using only the dominant non-desired
receive signals as the denominator. The dominant non-desired
receive signals are the receive signals other than the desired
receive signal having a correlated power level above a threshold
level P.sub.T (such as 20 dB). In the present illustration, signals
B, C and D are the dominant non-desired receive signals and their
correlated powers are summed to be used as the denominator of the
metric. Signal E, on the other hand, has a correlated power level
less than the threshold level P.sub.T and is therefore not included
in the metric computation. The denominator of the metric, whether
computed using some or all of the receive signals other than the
desired receive signals, establishes the non-desired signal level
received at the repeater.
[0064] Accordingly, in one embodiment, the metric for antenna
weight adaptation is given as:
Metric = Pwr ( A ) 2 Pwr ( all above P T ) , ##EQU00001##
where Pwr(A) denotes the correlated power of the desired receive
signal with the largest correlated power and Pwr(all above P.sub.T)
denotes the correlated power of all other receive signals having a
correlated power greater than the threshold level P.sub.T, also
referred as the dominant non-desired receive signals. The
above-described metric can then be optimized using various adaptive
metric optimization algorithms, such as steepest descent based
algorithms.
[0065] In the present embodiment, the metric is computed by using
all dominant non-desired receive signals. In other embodiments,
only some or a subset of the dominant non-desired receive signals
are summed for use as the denominator of the metric. It is not
critical to use all of the dominant non-desired receive signals in
the metric computation.
[0066] FIG. 9 illustrates the correlated power computed for
incoming signals received at a repeater employing an antenna array
in an operating environment including multiple signal sources, such
as multiple base stations, according to another embodiment of the
present invention. In the present illustration, the repeater is
assumed to determine the array weights before echo cancellation or
does not implement echo cancellation. The incoming feedback
signals, if any, have not been echo cancelled before the array
weights are to be determined Referring to FIG. 9, the repeater
receives multiple incoming signals corresponding to various pilot
code phases or various PN code offsets. The receive signals include
feedback signals from the repeater itself. In one embodiment, a
metric for antenna weight adaptation is constructed by using the
correlated power of the desired receive signal as the numerator.
Before echo cancellation is performed or when echo cancellation is
not performed, the feedback signal from the repeater (signal F)
will be the signal with the largest correlated energy. In that
case, the desired receive signal is selected by searching for the
signal with the largest correlated power a delay D prior to the
signal with the overall largest correlated power level, the signal
with the overall largest correlated power being the feedback
signal, where delay D represents the delay through the repeater. In
the present illustration, signal G is the signal with the largest
correlated power a repeater delay D prior to the largest feedback
signal F. Thus, signal G is selected as the desired receive signal.
More specifically, in one embodiment, the absolute value of the
correlated power of the desired receive signal is taken and is
squared to use as the numerator of the metric.
[0067] In one embodiment, the metric for antenna weight adaptation
is constructed using the sum of the correlated power of all other
receive signals as the denominator. In another embodiment, an
enhanced metric is provided where the metric is constructed using
only the dominant non-desired receive signals as the denominator.
The dominant non-desired receive signals are the receive signals
other than the desired receive signal having a correlated power
level above a threshold level P.sub.T (such as 20 dB). In the
present illustration, all other receive signals except for signal H
are the dominant non-desired receive signals and their correlated
powers are summed to be used as the denominator of the metric.
[0068] In this manner, a metric for antenna weight adaptation is
constructed using the desired receive signal with the largest
correlated power excluding the feedback signal as the numerator and
using the other correlated power above a given threshold as the
denominator. In one embodiment, the metric is given as:
Metric = Pwr ( G ) 2 Pwr ( all about P T ) , ##EQU00002##
where Pwr(G) denotes the correlated power of the desired receive
signal with the largest correlated power, excluding the feedback
signal, and Pwr(all above P.sub.T) denotes the correlated power of
all other receive signals having a correlated power greater than
the threshold level P.sub.T, also referred as the dominant
non-desired receive signals. The above-described metric can then be
optimized using various adaptive metric optimization algorithms,
such as steepest descent based algorithms.
[0069] In the present embodiment, the metric is computed by using
all dominant non-desired receive signals. In other embodiments,
only some or a subset of the dominant non-desired receive signals
are summed for use as the denominator of the metric. It is not
critical to use all of the dominant non-desired receive signals in
the metric computation.
[0070] In some embodiments of the present invention, a steepest
descent algorithm is applied to optimize the above-described
metrics. The steepest descent algorithm is applied recursively to
compute the weights for the antenna elements to maximize the
metric, thereby maximizing the SNR or E.sub.C/I.sub.0 of the
desired receive signal. In general, the steepest descent algorithm
refers to an algorithm for numerically finding the minimum value of
a function (the metric), based on the gradient of the function.
Each successive iteration of the algorithm moves along the
direction where the function is increasing or decreasing most
rapidly and recomputes the gradient to determine the new direction
to travel.
[0071] According to one aspect of the present invention, the
adaptive metric optimization algorithm is applied for both echo
cancellation and for interference reduction. That is, the metric is
optimized to reduce the feedback signal as well as to reduce the
interference from neighboring signal sources. More specifically,
when the total SNR or E.sub.C/I.sub.0 is maximized, the array
weights will also effectively reduce the feedback signal to desired
receive signal level.
[0072] Implementations of the antenna weight computation method in
a wireless repeater using either the error minimizing approach or
the SNR maximizing approach will now be described in more
detail.
Array Weight Computation Using Error Minimizing Algorithms
[0073] FIG. 10 is a schematic diagram of a repeater employing an
antenna array and employing echo cancellation after the antenna
weights are determined using the antenna weight computation method
according to one embodiment of the present invention. FIG. 11 is a
flowchart illustrating the antenna weight computation method
implemented in the repeater of FIG. 10 using closed form MMSE
algorithm according to one embodiment of the present invention. The
antenna weight computation method of FIG. 11 is referred to as
"MMSE Combine then Cancel" to refer to the use of closed form
calculation with a MMSE algorithm in a repeater that combine the
array data before performing echo cancellation. The operation of
the MMSE Combine then Cancel antenna weight computation method 800
as implemented in repeater 1200 will now be described with
reference to both FIGS. 10 and 11.
[0074] Repeater 1200 includes an antenna array formed by a first
antenna element 1202 and a second antenna element 1204. First and
second receiver circuits RCVR1 and RCVR2 (1206, 1208) are coupled
to the first and second antenna elements respectively. Method 800
receives incoming signals from the operating environment on M
receiver circuits (RCVR1, RCVR2) associated with M antenna elements
1202, 1204 of the antenna array (step 802). The incoming signals
can include remote signals from nearby base stations and feedback
signals from the repeater's own antennas.
[0075] The incoming signals are provided to correlation blocks 1214
and 1216 to compute the correlation of the incoming signals with
known pilot signals (or pilot code phases). In the present
embodiment, the correlation is performed in the frequency domain
and thus correlation blocks 1214 and 1216 include storage elements
to store an FFT (Fast Fourier Transform) block of data for each
receiver circuit (step 804). Then, method 800 performs
cross-correlation of the receive signals with the known pilot
signals or pilot code phases in frequency domain (step 806). The
correlation results are then used to compute the array weights
W.sub.1 and W.sub.2 (complex) using closed form calculation with a
MMSE algorithm as follows. First, method 800 selects the desired
receive signal being the receive signal a given delay prior to the
receive signal with the overall largest correlated energy, the
signal with the overall largest correlated energy being the
feedback signal (step 808). The amount of delay is determined by
the signal delay through repeater 1200. The correlation blocks 1214
and 1216 can be implemented in software, hardware, firmware or a
combination thereof, including signal processors.
[0076] Once the desired receive signal is selected, the array
weights W.sub.1 and W.sub.2 for the antenna elements 1202, 1204 are
calculated at MMSE algorithm blocks 1215, 1217 (step 810). MMSE
algorithm blocks 1215, 1217 can be implemented as signal
processors, such as digital signal processors and can include
memory and computational elements. More specifically, method 800
calculates the array weights W.sub.1 and W.sub.2 for the antenna
elements 1202, 1204 using a MMSE algorithm to minimize the mean
square error between the desired receive signal and the associated
pilot signal or pilot code phase.
[0077] When array weights W.sub.1 and W.sub.2 are determined, they
are provided to multipliers 1210 and 1212 to multiply the
respective receive signals, thereby steering the antenna reception.
Multipliers 1210 and 1212 can be implemented as data converters and
can also be implemented in software, hardware or firmware or a
combination thereof. The weighted receive signals are then combined
at combiner 1218 (step 812). The combined receive signal is then
provided to echo canceller 1220 for echo cancellation (step 814).
The echo cancelled signal is amplified by variable gain amplifier
1222 and provided to the transmitter circuit 1224 for transmission
on an antenna element 1226 (step 816). Method 800 can then be
repeated for the next FFT block of data from the incoming signals
(step 818).
[0078] FIG. 12 is a schematic diagram of a repeater employing an
antenna array and employing echo cancellation before the antenna
weights are determined using the antenna weight computation method
according to one embodiment of the present invention. FIG. 13 is a
flowchart illustrating an antenna weight computation method
implemented in the repeater of FIG. 12 using closed form MMSE
algorithm according to one embodiment of the present invention. The
antenna weight computation method of FIG. 13 is referred to as
"MMSE Cancel then Combine" to refer to the use of closed form
calculation with a MMSE algorithm in a repeater that perform echo
cancellation before combining the array data. The operation of the
MMSE Cancel then Combine antenna weight computation method 900 as
implemented in repeater 1300 will now be described with reference
to both FIGS. 12 and 13.
[0079] Repeater 1300 includes an antenna array formed by a first
antenna element 1302 and a second antenna element 1304. First and
second receiver circuits RCVR1 and RCVR2 (1306, 1308) are coupled
to the first and second antenna elements respectively. Method 900
receives incoming signals from the operating environment on M
receiver circuits (RCVR1, RCVR2) associated with M antenna elements
1302, 1304 of the antenna array (step 902). The incoming signals
can include remote signals from nearby base stations and feedback
signals from the repeater's own antennas.
[0080] The incoming signals at each receiver circuit 1306, 1308 are
provided to echo cancellers 1310, 1312 for echo cancellation where
the feedback signal components of the incoming signals are removed
or substantially removed (step 904). The echo-cancelled signals are
then provided to correlation blocks 1318 and 1320 to compute the
correlation of the echo-cancelled signals with known pilot signals
or known pilot code phases. In the present embodiment, the
correlation is performed in the frequency domain and thus
correlation blocks 1318 and 1320 include storage elements to store
an FFT (Fast Fourier Transform) block of data for each receiver
circuit (step 906). Then, method 900 performs cross-correlation of
the receive signals with known pilot signal or known pilot code
phases in frequency domain (step 908). The correlation results are
then used to compute the array weights W.sub.1 and W.sub.2 using
closed form calculation with a MMSE algorithm as follows. First,
method 900 selects the desired receive signal being the receive
signal having the largest correlated energy (step 910).
[0081] Once the desired receive signal is selected, the array
weights W.sub.1 and W.sub.2 for the antenna elements 1302, 1304 are
calculated at MMSE algorithm blocks 1319, 1321 (step 912). More
specifically, method 900 calculates the array weights W.sub.1 and
W.sub.2 for the antenna elements 1302, 1304 using a MMSE algorithm
to minimize the mean square error between the desired receive
signal and the associated pilot signal or pilot code phases.
[0082] When array weights W.sub.1 and W.sub.2 are determined, they
are provided to multipliers 1314 and 1316 to multiply the
respective echo-cancelled signals, thereby steering the antenna
reception (step 914). The weighted echo-cancelled signals are then
combined at combiner 1322. The combined signal is amplified by
variable gain amplifier 1324 and provided to the transmitter
circuit 1326 for transmission on an antenna element 1328 (step
916). Method 900 can then be repeated for the next FFT block of
data from the incoming signals (step 918).
Array Weight Computation Using Adaptive Metric Optimization
[0083] FIG. 14 is a schematic diagram of a repeater employing an
antenna array and employing echo cancellation after the antenna
weights are determined using the antenna weight computation method
according to one embodiment of the present invention. FIG. 15 is a
flowchart illustrating an antenna weight computation method
implemented in the repeater of FIG. 14 using a metric with a metric
optimization algorithm according to one embodiment of the present
invention. The antenna weight computation method of FIG. 15 is
referred to as "Metric/Steepest Descent Combine then Cancel" to
refer to the use of a metric with a steepest descent algorithm in a
repeater that combine the array data before performing echo
cancellation. The operation of the Metric/Steepest Descent Combine
then Cancel antenna weight computation method 1000 as implemented
in repeater 1400 will now be described with reference to both FIGS.
14 and 15.
[0084] Repeater 1400 includes an antenna array formed by a first
antenna element 1402 and a second antenna element 1404. First and
second receiver circuits RCVR1 and RCVR2 (1406, 1408) are coupled
to the first and second antenna elements respectively. Method 1000
receives incoming signals from the operating environment on M
receiver circuits (RCVR1, RCVR2) associated with M antenna elements
1402, 1404 of the antenna array (step 1002). The incoming signals
can include remote signals from nearby base stations and feedback
signals from the repeater's own antennas.
[0085] The incoming signals are provided to multipliers 1414 and
1416 to be multiplied with the respective array weights W.sub.1 and
W.sub.2, thereby steering the antenna reception (step 1004).
Because antenna weight computation method 1000 is an adaptive
computation method, the antenna weights are recursively calculated
to optimize the metric. Therefore, at any point in the operation of
repeater 1400, the most recently computed values for array weights
W.sub.1 and W.sub.2 are used at multipliers 1414, 1416. The values
for array weights W.sub.1 and W.sub.2 are updated at each metric
optimization calculation.
[0086] The weighted receive signals are then combined at combiner
1418. The combined receive signal is then provided to echo
canceller 1420 for echo cancellation (step 1006). The echo
cancelled signal is amplified by variable gain amplifier and
provided to the transmitter circuit 1422 for transmission on an
antenna element 1424 (step 1008).
[0087] Meanwhile, the combined receive signal, before echo
cancellation, is provided to a correlation block 1410 to compute
the correlation of the combined receive signal with known pilot
codes or known pilot code phases. In the present embodiment, the
correlation is performed in the frequency domain and thus
correlation block 1410 includes storage elements to store an FFT
(Fast Fourier Transform) block of data for each receiver (step
1010). Then, method 1000 performs cross-correlation of the receive
signals with known pilot codes or known pilot code phases in
frequency domain (step 1012). The correlation results are then
provided to metric generation and optimization block 1412 to
compute the array weights W.sub.1 and W.sub.2 using a metric and a
metric optimization algorithm as follows. Metric generation and
optimization block 1412 can be implemented as signal processors,
such as digital signal processors and can include memory and
computational elements.
[0088] First, method 1000 selects the desired receive signal being
the receive signal a given delay prior to the receive signal with
the overall largest correlated energy, the signal with the overall
largest correlated energy being the feedback signal (step 1014).
The amount of delay is determined by the signal delay through
repeater 1400. Then, a metric is computed based on the desired
receive signal (step 1016). In one embodiment, the metric is given
as the ratio of the correlated power of the desired receive signal
to the sum of the correlated power of all or some of the other
receive signals. Then, a metric optimization algorithm, such as a
steepest descent adaptive algorithm is applied to adaptively
compute the array weights W.sub.1 and W.sub.2 for the antenna
elements 1402, 1404 with the goal of optimizing the metric (step
1018). The computed array weights W.sub.1 and W.sub.2 are then
provided to multipliers 1414 and 1416 to apply the newly calculated
array weights to the incoming receive signals. Method 1000 can then
be repeated for the next FFT block of data to update the metric
computation (step 1020). The steepest descent algorithm is
recursively apply to compute the array weights while the metric is
optimized.
[0089] FIG. 16 is a schematic diagram of a repeater employing an
antenna array and employing echo cancellation before the antenna
weights are determined using the antenna weight computation method
according to one embodiment of the present invention. FIG. 17 is a
flowchart illustrating an antenna weight computation method
implemented in the repeater of FIG. 16 using a metric with a metric
optimization algorithm according to one embodiment of the present
invention. The antenna weight computation method of FIG. 17 is
referred to as "Metric/Steepest Descent Cancel then Combine" to
refer to the use of a metric with a metric optimization algorithm
in a repeater that perform echo cancellation before combining the
array data. The operation of the Metric/Steepest Descent Cancel
then Combine adaptive antenna weight computation method 1100 as
implemented in repeater 1500 will now be described with reference
to both FIGS. 16 and 17.
[0090] Repeater 1500 includes an antenna array formed by a first
antenna element 1502 and a second antenna element 1504. First and
second receiver circuits RCVR1 and RCVR2 (1506, 1508) are coupled
to the first and second antenna elements respectively. Method 1100
receives incoming signals from the operating environment on M
receiver circuits (RCVR1, RCVR2) associated with M antenna elements
1502, 1504 of the antenna array (step 1102). The incoming signals
can include remote signals from nearby base stations and feedback
signals from the repeater's own antennas.
[0091] The incoming signals at each receiver circuit 1506, 1508 are
provided to echo cancellers 1510, 1512 for echo cancellation where
the feedback signal components of the incoming signals are removed
or substantially removed (step 1104). The echo-cancelled receive
signals are provided to multipliers 1518 and 1519 to be multiplied
with the respective array weights W.sub.1 and W.sub.2, thereby
steering the antenna reception (step 1106). The weighted
echo-cancelled signals are then combined at combiner 1520. The
combined signal is amplified by variable gain amplifier 1522 and
provided to the transmitter circuit 1524 for transmission on an
antenna element 1526 (step 1108). Array weights W.sub.1 and W.sub.2
are recursively calculated to optimize the metric. Therefore, at
any point in the operation of repeater 1500, the most recently
computed values for array weights W.sub.1 and W.sub.2 are used at
multipliers 1518, 1519. The values for array weights W.sub.1 and
W.sub.2 are updated at each metric optimization calculation.
[0092] Meanwhile, the combined echo-cancelled receive signal is
provided to a correlation block 1514 to compute the correlation of
the combined echo-cancelled signal with known pilot codes or known
pilot code phases. In the present embodiment, the correlation is
performed in the frequency domain and thus correlation block 1514
includes storage elements to store an FFT (Fast Fourier Transform)
block of data for each receiver (step 1110). Then, method 1100
performs cross-correlation of the receive signals with known pilot
codes or known pilot code phases in frequency domain (step 1112).
The correlation results are then provided to metric generation and
optimization block 1516 to compute the array weights W.sub.1 and
W.sub.2 using a metric and a metric optimization algorithm as
follows.
[0093] First, method 1100 selects the desired receive signal being
the receive signal having the largest correlated energy (step
1114). Then, a metric is computed based on the desired receive
signal (step 1116). In one embodiment, the metric is given as the
ratio of the correlated power of the desired receive signal to the
sum of the correlated power of all or some of the other receive
signals. Then, a metric optimization algorithm, such as a steepest
descent adaptive algorithm is applied to adaptively compute the
array weights W.sub.1 and W.sub.2 for the antenna elements 1502,
1504 with the goal of optimizing the metric (step 1118). The
computed array weights W.sub.1 and W.sub.2 are then provided to
multipliers 1518 and 1519 to apply the newly calculated array
weights to the incoming receive signals. Method 1100 can then be
repeated for the next FFT block of data to update the metric
computation (step 1120). The steepest descent algorithm is
recursively apply to compute the array weights while the metric is
optimized.
Antenna Array with Vertical and Horizontal Feeds
[0094] Referring again to FIG. 1, in some configurations, the patch
antennas 410 and 415 can be operated in two modes. More
specifically, the patch antennas 410 and 415 can each be operated
in a vertical feed mode and a horizontal feed mode. Accordingly, on
each side of PCB 405, there are effectively four antennas--two
vertical feed antennas and two horizontal feed antennas. The
antenna configuration 400 in FIG. 1 can thus operate with eight
antennas, where four antennas are in the vertical feed mode and
four antennas are in the horizontal feed mode.
[0095] According to one aspect of the present invention, an echo
cancellation repeater employing antenna arrays includes antenna
elements for vertical feed mode and antenna elements for horizontal
feed modes where the antenna elements are switchably connected to
select a combination of antenna elements for the receive side and
the transmit side to obtain the desired performance result. In some
embodiments, the repeater implements an antenna weight computation
method to compute antenna weights for each combination of antenna
elements. Performance results for different combinations of antenna
elements are compared to select the antenna element combination
providing the best desired performance result. Accordingly, a
combination of antenna elements is selected to steer the reception
and transmission of the antenna arrays so that the repeater with
the antenna arrays can be operated to reduce interference and
improve signal reception.
[0096] In some embodiments, the desired performance result is
measured by one or more performance factors and multiple
performance factors may be weighted to tailor the performance
result for specific applications. The performance factors can
include the quality of the receive signal, the quality of the
channel or the amount of feedback signals. Other performance
factors can also be used to define the desired performance result
to be obtained.
[0097] In embodiments of the present invention, an echo
cancellation repeater with switchably connected antenna elements is
implemented by switchably connecting two or more antenna elements
to a single transceiver circuit. Accordingly, a smaller number of
transceiver circuits is required to support a large number of
antenna elements. The repeater with switchably connected antenna
elements provides an advantage in that the repeater can be provided
with a large number of antenna elements while maintaining a small
form factor and reduced weight and complexity.
[0098] According to another aspect of the present invention, an
echo cancellation repeater employing antenna arrays includes
antenna elements for vertical feed mode and antenna elements for
horizontal feed modes where each antenna element is coupled to a
transceiver circuit. The repeater applies beamforming techniques in
baseband to select the desired antenna elements and to change the
spatial selectivity of the antenna arrays to obtain the desired
performance result. In some embodiments, antenna weights for the
receiver and the transmitter are determined in baseband to combine
signals from the antenna elements to achieve the desired
directionality of the array. In some embodiments, the desired
performance result is measured by one or more performance factors
and multiple performance factors may be weighted to tailor the
performance result for specific applications.
Antenna Array with Switchably Connected Antenna Elements
[0099] FIG. 18 illustrates an echo cancellation repeater 1600
operative to perform signal conditioning and amplification using
one or more antenna arrays according to embodiments of the present
invention. Repeater 1600 includes a first antenna array 1605
disposed, for example, on a first side of the antenna configuration
and a second antenna array 1640 disposed, for example, on a second
side of the antenna configuration. The first antenna array 1605
includes antenna elements 1612, 1614 which can be formed as a patch
antenna, and antenna elements 1616, 1618 which can be formed as
another patch antenna. The second antenna array includes antenna
elements 1632, 1634 which can be formed as a patch antenna, and
antenna elements 1636 and 1638 which can be formed as another patch
antenna. In each patch antenna, a first antenna element (such as
element 1612 and 1616) is disposed for vertical feel mode while a
second antenna element (such as element 1614 and 1618) is disposed
for horizontal feed mode.
[0100] The repeater 1600 further includes a processing circuitry
1645 including multiple transceiver circuits 1620 and a controller
and baseband circuit 1625. The antenna arrays 1605 and 1640
cooperate with the multiple transceiver circuits 1620 which
cooperates with controller and baseband circuit 1625 as part of
operations of repeater 1600. In operation, incoming signals can be
received by antenna array 1605 or 1640 and passed to processing
circuitry 1645 for signal conditioning and processing and then
passed back to the other antenna array 1605 or 1640 for
transmission as outgoing signals. For instance, the incoming
signals may come from a base station of a CDMA wireless
communications network and the outgoing signals may be intended for
a mobile device within the repeater's range. In the present
embodiment, the processing circuitry 1645 performs echo
cancellation as part of the signal conditioning and processing
operation. It is imperative to note that the number and
configuration of the antenna arrays described herein are merely
illustrative as the herein described repeater systems and methods
contemplate use of varying number of antenna arrays having varying
configurations and comprising varying number of antenna
elements.
[0101] In the present embodiment, the antenna elements in the first
and second antenna arrays 1605 and 1640 are coupled to switches to
allow the antenna elements to be individually selected to steer the
antenna reception. In the present embodiment, a pair of vertical
feed and horizontal feed antennas is coupled to a switch so that
the eight antennas are coupled to four transceiver circuits through
four switches. For instance, in the first antenna array 1605, a
switch 1611 is coupled to select between vertical feed antenna
element 1612 and horizontal feed antenna element 1614 and another
switch 1615 is coupled to select between vertical feed antenna
element 1616 and horizontal feed antenna element 1618. The second
antenna array 1640 is constructed in a similar manner with switches
1631 and 1635 coupled to the antenna elements to select between
antenna elements 1632 and 1634 and to select between antenna
elements 1636 and 1638.
[0102] In repeater 1600, the selected antenna elements are
connected to transceiver circuits 1620 in the processing circuitry
1645. In the present embodiment, the repeater 1600 includes four
switches coupled to select a combination four antenna elements out
of the eight antenna elements. The selected antenna element for
each switch is coupled to a transceiver circuit. Thus, four
transceiver circuits XCV1 to XCV4 are provided to cooperate with
the four switches selecting a combination of antenna elements. Each
transceiver circuit includes a receiver circuit to receive the
incoming receive signal from the associated antenna element and a
transmitter circuit to provide the outgoing transmitted signal to
the associated antenna element.
[0103] In operation, switches 1611, 1615, 1631 and 1635 are
controlled by the controller and baseband circuit 1625 to select a
combination of four out of eight antenna elements. The selected
combination of antenna elements may include antenna elements of the
same feed; that is, all vertical feed or all horizontal feed. The
selected combination may also include antenna elements of either
the vertical or the horizontal feed. Thus, in repeater 1600,
sixteen combination of antenna elements are possible. In other
embodiments, the repeater may be provided with different number of
antenna elements in each antenna array and the antenna array may
have different configurations, such as three antenna elements
coupled to a switch. The exact number of antenna elements or
configuration of the antenna elements is not critical to the
practice of the present invention.
[0104] In accordance with embodiments of the present invention,
repeater 1600 implements the antenna element selection method of
the present invention to select a combination of antenna elements
from the antenna arrays for reception and transmission so as to
obtain the best desired performance result. Furthermore, repeater
1600 applies the antenna weight computation method described above
to determine antenna weights for the selected combination of
antenna elements to modify the spatial selectivity of the antenna
array so as to steer the antenna array of the repeater to be more
receptive to transmission from a desired direction, thereby
reducing signal interference and improving reception quality.
[0105] In an antenna array, the signal from each antenna element
can be multiplied by a different weight to achieve the desired
antenna spatial selectivity. In the present description, array
weights refer to the complex values (e.g. W=a+jb) used to multiply
the receive signal of each antenna element. The weighted receive
signals of all the antenna elements are combined to form the
antenna beam. When the array weights are chosen properly, the
antenna beam can be steered in such a way so as to cancel energy
from undesirable directions and emphasis energy from desired
directions. That is, the antenna beam can be steered by changing
the antenna weights to change the direction of maximum
reception.
[0106] FIG. 19 is a flow chart illustrating an antenna element
selection method incorporating the antenna weight computation
method implemented in an echo cancellation repeater employing
antenna arrays for improving signal reception according to one
embodiment of the present invention. Referring to FIG. 19, antenna
element selection method 1700 is implemented in a repeater
employing a first antenna array including horizontal feed and
vertical feed antenna elements and a second antenna array including
horizontal feed and vertical feed antenna elements. In operation,
one antenna array is receiving incoming signals while the other
antenna array is transmitting outgoing signals. The antenna
elements of both antenna arrays are switchably connected to
transceiver circuits of the repeater to process incoming and
outgoing signals. The antenna element selection method enables the
selection of a combination of antenna elements from the two antenna
arrays to obtain the best performance results.
[0107] At step 1701, a combination of P antenna elements from the
first and second antenna arrays is selected. The P antenna elements
can include any number of vertical feed or horizontal feed antenna
elements from the first and second antenna arrays. Then, at step
1702, the repeater receives incoming signals from the operating
environment on the receiver circuits associated with selected
antenna elements of the receiving antenna array. The incoming
signals can include remote signals from nearby base stations and
the feedback signal from the repeater's own antennas. The repeater
may perform echo cancellation at this stage or the repeater may
perform echo cancellation after the antenna array weights are
calculated and the incoming signals from the different antenna
elements are combined.
[0108] Method 1700 performs correlation of the receive signals with
one or more reference signals (step 1704). When the repeater is
deployed in a CDMA based communication system, the reference
signals are the known pilot signals or known pilot codes or known
pilot code phases of the base stations in the system. Pilot code
phases refer to the same pilot code with known code offsets. When
the repeater is deployed in a WCDMA based communication system, the
reference signals are the known scrambling codes of the base
stations in the system. Finally, when the repeater is deployed in a
non-CDMA based communication system, the reference signals are some
or all of the pilot tones in an OFDM symbol or an OFDM preamble. In
other communication systems, the known pilot codes or pilot signals
used in those systems can be used as the reference signals. Method
1700 computes the correlated power or correlated energy of the
receive signals corresponding to the one or more reference signals,
such as one or more pilot codes or pilot tones.
[0109] After computing the correlated power of the receive signals,
method 1700 selects a desired receive signal being the receive
signal, other than the feedback signal, having the largest
correlated power with a reference signal, such as a known pilot
code phase (step 1706). That is, the desired receive signal is
selected from the receive signals excluding the leakage or feedback
signals at the repeater, if any. It is instructive to note that in
some embodiments, the antenna weights are determined after echo
cancellation is carried out, while in other embodiments, the
antenna weights are determined before echo cancellation. In the
case when antenna weights are determined before echo cancellation,
the largest correlated power detected by method 1700 could be the
feedback signal from the repeater itself. Any leakage or feedback
signals should be excluded when selecting the desired receive
signal. Accordingly, in one embodiment, the desired receive signal
is determined by searching for the signal with the largest
correlated power a delay D prior to the signal with the overall
largest correlated power level, the signal with the overall largest
correlated power being the feedback signal, where delay D
represents the delay through the repeater.
[0110] Once the desired receive signal is selected, method 1700
determines the weights to be used with each of the P antenna
elements (the "array weights") in order to steer the antenna beam
for improving spatial selectivity. The array weights, including
receive antenna weights and transmit antenna weights, can be
determined using various algorithms and metrics.
[0111] In some embodiments, the array weights are determined by
minimizing the error between the desired receive signal and the
reference signal (step 1708). More specifically, in some
embodiments, the array weights are calculated in closed form using
an error minimizing algorithm (step 1710). In one embodiment,
closed form calculation using a minimum mean square error (MMSE)
algorithm is used to determine the array weights. More
specifically, the antenna weights are computed in closed form to
minimize the mean square error between the desired receive signal
and the reference signal (the known pilot signal or pilot code
phase). The MMSE algorithm is applied to select antenna weights so
that the desired receive signal looks as close as possible to the
reference signal in phase and in magnitude. In other embodiments,
other closed form algorithm can be used to compute the array
weights.
[0112] In alternate embodiments, the array weights are determined
adaptively to maximize the signal-to-noise ratio (SNR) of the
desired receive signal (step 1712). In some embodiments, the array
weights are computed recursively using a metric and an adaptive
metric optimization algorithm (step 1714). That is, a metric is
provided to estimate the SNR of the desired receive signal and the
antenna weights are recursively computed to optimize the
predetermined metric. In some embodiments, the metric used is the
ratio of the correlated power of the desired receive signal to the
sum of the correlated power of some or all of the other receive
signals. In one embodiment, the metric sums only the dominant
non-desired receive signals as the denominator of the ratio where
the dominant non-desired receive signals refer to receive signals
other than the desired receive signal having a correlated power
level above a predetermined threshold. Furthermore, in one
embodiment, a steepest descent algorithm is used to recursively
determine the antenna weights while optimizing the metric. The use
of a steepest descent algorithm is illustrative only. In other
embodiments, other adaptive metric optimization algorithm can be
used.
[0113] It is imperative to note that the error minimizing
computation method (steps 1708-1710) and the SNR maximizing
computation method (steps 1712-1714) represent alternate methods
for determining the array weights of the receiving antenna array.
They are both shown in the flowchart of FIG. 19 to illustrate the
alternate methods but method 1700 can be implemented with one or
the other array weight computation method and does not need to
implement both array weight computation methods at the same
time.
[0114] After the array weights for the currently selected antenna
element combination are computed, method 1700 stores the array
weights and also stores the performance result for the currently
selected antenna element combination (step 1716). The performance
result can be derived from one or more performance factors. The
performance factors can include the amount of feedback signal, the
quality of the channel and the signal-to-noise ratio (SNR) of the
receive signals. After the array weights and the performance result
for the currently selected antenna element combination are stored,
method 1700 proceeds to determine if all combinations of antenna
elements have been selected (step 1718). If not all combinations
have been evaluated, method 1700 proceeds to select another
combination of P antenna elements from the first and second antenna
arrays (step 1720). Method 1700 returns to step 1702 where the
incoming signals are received on the receiver circuits of the
selected antenna elements.
[0115] Method 1700 continues until all combinations of antenna
elements have been selected and the array weights and performance
results have been stored for all antenna element combinations.
Then, a desired combination of antenna elements is selected based
on the best desired performance results (step 1720). Accordingly, a
combination of antenna elements is selected to steer the reception
and transmission of the antenna arrays so that the repeater with
the antenna arrays can be operated to reduce interference and
improve signal reception.
[0116] As described above, the performance result can be derived
from one or more performance factors. In embodiments of the present
invention, the performance factors can include the amount of
feedback signal from the transmitter. Accordingly, the desired
performance result can be expressed as the antenna element
combination that gives the lowest feedback signal from the
transmitter.
[0117] Another performance factor includes the quality of the
channel and the ease of cancelling the feedback signal from the
channel. The desired performance result can be an antenna element
combination that gives a channel with a high degree of ease of
feedback cancellation. Another performance factor includes the
quality of the receive signal as measured by the signal-to-noise
ratio (SNR). The desired performance result can be an antenna
element combination that gives a receive signal with the best SNR
or the best match to a desired reference. Other performance factors
are can also be used and the performance factors described herein
are illustrative only and are not intended to be limiting.
[0118] In method 1700, all combination of antenna elements from the
antenna arrays are evaluated to select the desired combination of
antenna elements. In other embodiments, the antenna element
selection method can be implemented to evaluate only a subset of
the combination of antenna elements. It is not critical to evaluate
all possible combinations of antenna elements.
Array with Vertical and Horizontal Feed Antenna Elements
[0119] FIG. 20 illustrates an echo cancellation repeater 1650
operative to perform signal conditioning and amplification using
one or more antenna arrays according to embodiments of the present
invention. Repeater 1650 is constructed in a similar manner as
repeater 1600 of FIG. 18 and includes a first antenna array 1605
disposed on a first side of the antenna configuration and a second
antenna array 1640 disposed on a second side of the antenna
configuration. In operation, one antenna array is disposed for
receiving incoming signals while the other antenna array is
disposed for transmitting outgoing signals. Furthermore, each of
the first and second antenna arrays include antenna elements for
the vertical feed mode and the horizontal feed mode. However, in
repeater 1650, the antenna elements are not switchably connected to
the transceiver circuits. Rather, the processing circuitry 1645
includes transceiver circuits 1620 for each antenna element. More
specifically, a bank of transceiver circuits XCV1 to XCV8 in the
multiple transceiver circuit 1620 is provided. Each transceiver
circuit is associated with a single antenna element. More
specifically, each of transceiver circuits XCV1 to XCV8 is coupled
to a vertical feed or horizontal feed antenna element 1612, 1614,
1616, 1618, 1632, 1634, 1636 or 1638. Repeater 1650 applies
beamforming techniques in baseband to select the desired antenna
elements and to change the spatial selectivity of the antenna
arrays to obtain the desired performance result.
[0120] FIG. 21 is a flow chart illustrating an antenna element
selection method incorporating the antenna weight computation
method implemented in an echo cancellation repeater employing
antenna arrays for improving signal reception according to one
embodiment of the present invention. The antenna element selection
method 1800 of FIG. 21 is applied to the repeater 1650 of FIG. 20
to perform selection of the antenna elements for reducing
interference and improving signal reception. Referring to FIG. 21,
at step 1802, the repeater receives incoming signals from the
operating environment on the receiver circuits associated with all
of the antenna elements of the receiving antenna array. The
incoming signals can include remote signals from nearby base
stations and the feedback signal from the repeater's own antennas.
The repeater may perform echo cancellation at this stage or the
repeater may perform echo cancellation after the antenna array
weights are calculated and the incoming signals from the different
antenna elements are combined.
[0121] Method 1800 performs correlation of the receive signals with
one or more reference signals (step 1804). When the repeater is
deployed in a CDMA based communication system, the reference
signals are the known pilot signals or known pilot codes or known
pilot code phases of the base stations in the system. Pilot code
phases refer to the same pilot code with known code offsets. When
the repeater is deployed in a WCDMA based communication system, the
reference signals are the known scrambling codes of the base
stations in the system. Finally, when the repeater is deployed in a
non-CDMA based communication system, the reference signals are some
or all of the pilot tones in an OFDM symbol or an OFDM preamble. In
other communication systems, the known pilot codes or pilot signals
used in those systems can be used as the reference signals. Method
1800 computes the correlated power or correlated energy of the
receive signals corresponding to the one or more reference signals,
such as one or more pilot codes or pilot tones.
[0122] After computing the correlated power of the receive signals,
method 1800 selects a desired receive signal being the receive
signal, other than the feedback signal, having the largest
correlated power with a reference signal, such as a known pilot
code phase (step 1806). That is, the desired receive signal is
selected from the receive signals excluding the leakage or feedback
signals at the repeater, if any. It is instructive to note that in
some embodiments, the antenna weights are determined after echo
cancellation is carried out, while in other embodiments, the
antenna weights are determined before echo cancellation. In the
case when antenna weights are determined before echo cancellation,
the largest correlated power detected by method 1800 could be the
feedback signal from the repeater itself. Any leakage or feedback
signals should be excluded when selecting the desired receive
signal. Accordingly, in one embodiment, the desired receive signal
is determined by searching for the signal with the largest
correlated power a delay D prior to the signal with the overall
largest correlated power level, the signal with the overall largest
correlated power being the feedback signal, where delay D
represents the delay through the repeater.
[0123] Once the desired receive signal is selected, method 1800
determines the weights to be used with each of the antenna elements
(the "array weights") in order to steer the antenna beam for
improving spatial selectivity. The array weights, including receive
antenna weights and transmit antenna weights, can be determined
using various algorithms and metrics.
[0124] In some embodiments, the array weights are determined by
minimizing the error between the desired receive signal and the
reference signal (step 1808). More specifically, in some
embodiments, the array weights are calculated in closed form using
an error minimizing algorithm (step 1810). In one embodiment,
closed form calculation using a minimum mean square error (MMSE)
algorithm is used to determine the array weights. More
specifically, the antenna weights are computed in closed form to
minimize the mean square error between the desired receive signal
and the reference signal (the known pilot signal or pilot code
phase). The MMSE algorithm is applied to select antenna weights so
that the desired receive signal looks as close as possible to the
reference signal in phase and in magnitude. In other embodiments,
other closed form algorithm can be used to compute the array
weights.
[0125] In alternate embodiments, the array weights are determined
adaptively to maximize the signal-to-noise ratio (SNR) of the
desired receive signal (step 1812). In some embodiments, the array
weights are computed recursively using a metric and an adaptive
metric optimization algorithm (step 1814). That is, a metric is
provided to estimate the SNR of the desired receive signal and the
antenna weights are recursively computed to optimize the
predetermined metric. In some embodiments, the metric used is the
ratio of the correlated power of the desired receive signal to the
sum of the correlated power of some or all of the other receive
signals. In one embodiment, the metric sums only the dominant
non-desired receive signals as the denominator of the ratio where
the dominant non-desired receive signals refer to receive signals
other than the desired receive signal having a correlated power
level above a predetermined threshold. Furthermore, in one
embodiment, a steepest descent algorithm is used to recursively
determine the antenna weights while optimizing the metric. The use
of a steepest descent algorithm is illustrative only. In other
embodiments, other adaptive metric optimization algorithm can be
used.
[0126] It is imperative to note that the error minimizing
computation method (steps 1808-1810) and the SNR maximizing
computation method (steps 1812-1814) represent alternate methods
for determining the array weights of the antenna array. They are
both shown in the flowchart of FIG. 21 to illustrate the alternate
methods but method 1800 can be implemented with one or the other
array weight computation method and does not need to implement both
array weight computation methods at the same time.
[0127] After the array weights for the currently selected antenna
element combination are computed, method 1800 then performs
beamforming to select a combination of antenna elements to obtain
the best desired performance result (step 1816). More specifically,
beamforming techniques are applied in baseband to adjust the
receive and transmit weights for all of the antenna elements of the
first and second antenna array so that a combination of antenna
elements is selected to obtain the best desired performance result.
The performance result can be derived from one or more performance
factors. The performance factors can include the amount of feedback
signal, the quality of the channel and the signal-to-noise ratio
(SNR) of the receive signals, as described above. In this manner,
the repeater 1650 is configured to operate with selected antenna
elements to give the desired directional signal transmission and
reception.
[0128] The communication system in which the repeater of the
present invention can be deployed includes various wireless
communication networks based on infrared, radio, and/or microwave
technology. Such networks can include, for example, a wireless wide
area network (WWAN), a wireless local area network (WLAN), a
wireless personal area network (WPAN), Worldwide Interoperability
for Microwave Access (Wi-max) and so on. A WWAN may be a Code
Division Multiple Access (CDMA) network, a Time Division Multiple
Access (TDMA) network, a Frequency Division Multiple Access (FDMA)
network, an Orthogonal Frequency Division Multiple Access (OFDMA)
network, a Single-Carrier Frequency Division Multiple Access
(SC-FDMA) network, and so on. A CDMA network may implement one or
more radio access technologies (RATs) such as CDMA2000,
Wideband-CDMA (W-CDMA), and so on. CDMA2000 includes IS-95,
IS-2000, and IS-856 standards. A TDMA network may implement Global
System for Mobile Communications (GSM), Digital Advanced Mobile
Phone System (D-AMPS), or some other RAT. GSM and W-CDMA are
described in documents from a consortium named "3rd Generation
Partnership Project" (3GPP). CDMA2000 is described in documents
from a consortium named "3rd Generation Partnership Project 2"
(3GPP2). 3GPP and 3GPP2 documents are publicly available. Other 3G
based wireless network can also be used. A WLAN may be an IEEE
802.11x network, and a WPAN may be a Bluetooth network, an IEEE
802.15x, or some other type of network. The systems and techniques
described herein may also be used for any combination of WWAN, WLAN
and/or WPAN.
[0129] Those skilled in the art will understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example: data, information,
signals, bits, symbols, chips, instructions, and commands may be
referenced throughout the above description. These may be
represented by voltages, currents, electromagnetic waves, magnetic
fields or particles, optical fields or particles, or any
combination thereof.
[0130] In one or more exemplary embodiments, the functions and
processes described may be implemented in hardware, software,
firmware, or any combination thereof. If implemented in software,
the functions may be stored on computer-readable medium. A storage
media may be any available media that can be accessed by a
computer. By way of example, and not limitation, such
computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or
other optical disk storage, magnetic disk storage or other magnetic
storage devices, or any other medium that can be used to store
desired program code in the form of instructions or data structures
and that can be accessed by a computer. Disk and disc, as used
herein, includes compact disc (CD), laser disc, optical disc,
digital versatile disc (DVD), floppy disk and blu-ray disc where
disks usually reproduce data magnetically, while discs reproduce
data optically with lasers. Combinations of the above should also
be included within the scope of computer-readable media. The term
"control logic" used herein applies to software (in which
functionality is implemented by instructions stored on a
machine-readable medium to be executed using a processor), hardware
(in which functionality is implemented using circuitry (such as
logic gates), where the circuitry is configured to provide
particular output for particular input, and firmware (in which
functionality is implemented using re-programmable circuitry), and
also applies to combinations of one or more of software, hardware,
and firmware.
[0131] For a firmware and/or software implementation, the
methodologies may be implemented with modules (e.g., procedures,
functions, and so on) that perform the functions described herein.
Any machine readable medium tangibly embodying instructions may be
used in implementing the methodologies described herein. For
example, software codes may be stored in a memory, for example the
memory of mobile station or a repeater, and executed by a
processor, for example the microprocessor of modem. Memory may be
implemented within the processor or external to the processor. As
used herein the term "memory" refers to any type of long term,
short term, volatile, nonvolatile, or other memory and is not to be
limited to any particular type of memory or number of memories, or
type of media upon which memory is stored. The term "machine
readable medium" does not embrace transitory propagating
signals.
[0132] Moreover, the previous description of the disclosed
implementations is provided to enable any person skilled in the art
to make or use the present invention. Various modifications to
these implementations will be readily apparent to those skilled in
the art, and the generic principles defined herein may be applied
to other implementations without departing from the spirit or scope
of the invention. Thus, the present invention is not intended to be
limited to the features shown herein but is to be accorded the
widest scope consistent with the principles and novel features
disclosed herein.
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